The Triplanar Hallux Abducto Valgus Classification System: Is it Valid?

Historically, 2-dimensional radiographic study techniques have been used to classify deformity and guide treatment of hallux valgus deformities in the transverse plane. Recently, a triplanar hallux abducto valgus classification system was proposed. The key elements of this classification system are the pathologic alignments in 3 anatomic planes. The triplanar hallux abducto valgus classification system is intended to clarify the deformity and apply a triplanar anatomic algorithm for treatment. To our knowledge, this classification system has not been validated. Our objective was to assess reliability of the triplanar hallux valgus classification system. Patients with hallux abducto valgus were identified from a foot and ankle registry. Digital radiographs were assembled in a digital slide presentation. The eligibility criteria required complete radiographic studies and represented varying degrees of hallux abducto valgus. The reviewers included 3 board-certified, fellowship-trained orthopedic foot and ankle surgeons. Each reviewer independently classified the hallux abducto valgus deformity for a total of 75 observations. After an 8-week washout period, the order of the hallux abducto valgus cases was randomized in the digital slide presentation and redistributed to the reviewers. The average kappa value from 3 readers was 0.241 with 95% CI (0.093-0.374), indicating a fair agreement. The inter-reader agreement was 0.046 with 95% CI (-0.041 to 0.112), showing poor agreement between readers. Our results indicate the triplanar hallux abducto valgus is not a reliable classification system. While this is the first known triplanar hallux abducto valgus classification system, it lacks prognostic value and reliability.